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Assessing the threat of non-native salmonids to Lahontan cutthroat trout recovery in a subalpine watershed
AuthorSmith, Jason Alan
AdvisorPeacock, Mary M.
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Introductions of non-native fishes complicate native fish recovery and introductions of non-native salmonids have been implicated in the decline of inland cutthroat trout subspecies. The United States Fish and Wildlife Service has been restocking Lahontan cutthroat trout Oncorhynchus clarkii henshawi in Fallen Leaf Lake, California annually since 2002 to stem this decline. Brown trout Salmo trutta pose a piscivory threat while rainbow trout O. mykiss and Lahontan cutthroat trout readily hybridize. Both rainbow trout and brown trout are found in Fallen Leaf Lake and the upper Glen Alpine Creek watershed which drains into the lake and therefore the presence of these species may represent significant threats to implementation of a successful reintroduction program. I investigated the genetic population structure and connectivity of naturalized rainbow and brown trout throughout the Glen Alpine Creek watershed including Fallen Leaf Lake in order to assess the threats posed by these non-native fishes. Fin clips were collected from adult rainbow trout (N=279) and brown trout (N= 350) for genetic analyses using electrofishing techniques in the stream network and gill-netting in the lakes within the watershed. Isolated DNA samples were genotyped at 13 (rainbow trout) and 10 (brown trout) polymorphic microsatellite loci. The Bayesian clustering program STRUCTURE was used to assess genetic connectivity. Using the delta k approach I found statistical support for three populations of rainbow and five populations of brown trout. Pairwise comparisons of these populations supported significant genetic differentiation and that this differentiation was associated with gradient barriers. Additionally, Mantel tests for both species showed some support for a pattern of isolation-by-distance. This study indicated genetic connectivity among rainbow and brown trout populations between the upper Glen Alpine Creek drainage and Fallen Leaf Lake populations, and identified a self-sustaining population of rainbow trout persisting in Fallen Leaf Lake. The results of this study have management implications and suggest that a watershed level recovery approach is necessary for the long term success of the reintroduction program for Lahontan cutthroat trout in Fallen Leaf Lake.